Electrodeposition of bone within a plastic matrix

ABSTRACT

A method of improving orthopedic implant material by the simultaneous electrodeposition of bone particles and an inert plastic binder onto a prosthesis is provided. A polyamic acid is dissolved in a solvent such as dimethylsulfoxide and an amine is added to the solution to produce the organic salt of a free carboxyl group. A colloidal suspension of the organic salt and fine bone particles in a mixed solvent comprised of acetone and dimethylsulfoxide is placed in a receptacle and a voltage is applied to a pair of electrodes immersed in the solution causing the deposition on the anode of bone in a polyamic acid plastic matrix. After subsequent cure, the result is a coating of bone within a polyimide matrix on the electrode.

United States Patent [1 1 Phillips et al.

[451 July 1,1975

[ ELECTRODEPOSITION OF BONE WITHIN A PLASTIC MATRIX [75] Inventors: David C. Phillips, Pittsburgh; Bevil J. Shaw, Murrysville, both of Pa.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: May 13, 1974 [21] Appl. No.: 469,181

[56] References Cited UNITED STATES PATENTS l/l97l Mizuguchi et all 204/181 2/197] Seiderman 204/l8l Primary Examiner-Howard S. Williams Attorney. Agent, or Firm-R. S. Sciascia; C. E. Vautrain, Jr.

[57] ABSTRACT A method of improving orthopedic implant material by the simultaneous electrodeposition of bone particles and an inert plastic binder onto a prosthesis is provided. A polyamic acid is dissolved in a solvent such as dimethylsulfoxide and an amine is added to the solution to produce the organic salt of a free carboxyl group. A colloidal suspension of the organic salt and fine bone particles in a mixed solvent comprised of acetone and dimethylsulfoxide is placed in a receptacle and a voltage is applied to a pair of electrodes immersed in the solution causing the deposition on the anode of bone in a polyamic acid plastic matrix. After subsequent cure, the result is a coating of bone within a polyimide matrix on the electrode.

20 Claims, N0 Drawings ELECTRODEPOSITION OF BONE WITHIN A PLASTIC MATRIX The present invention concerns the improvement of orthopedic implant materials and, more particularly, the anodic formation of bone coatings on prosthesis by electrodeposition of a composite of bone particles within a polyamic acid matrix which on subsequent heat cure results in bone particles within a polyimide plastic matrix. i

Advances in the field of total prosthetic replacement of bones include electrodepositing bone particles on prostheses and, also, coating such prosthesis by the rf sputtering process. The objective in such orthopedic implants is to determine a reliable and effective method The electrodeposition of some of the polyamic acids and their subsequent conversion to corresponding polyimides has been accomplished in the prior art. The teachings and techniques of such processes have not, however, been applied to the electrodeposition of particles of human or animal matter on prosthetic or other substrates. This application is the subject of the present invention. v

The formation of a colloidal suspension suitable for electrodeposition is a necessary precedent to at least one process for forming a coating on a prosthesis. According to the present invention, such a colloidal suspension is obtained by dissolving a commercially available polyamic acid such as Dupont Pyre-M.L. in a soland means for enhancing bone growth around the imi5 vent such as dimethylsulfoxide. An amine when added Plant and into the POres Ofthe implant Wail Enhancing to this solution produces an organic salt of free carbone growth is particularly important in bone-bridge boxy] groups which are present in the polyamic acid. operations where necrosis is inevitable if the bones are Th l i i h d to approximately 40C d not united in reasonable time- Often the bone p in maintained at this temperature for minutes. The for- Such cases is tallied with autogehous h but this 2O mer solution is added to a rapidly stirred non-solvent ally requires a second operation. In certain instances, uch as acetone and ground bone is then added to the the bone p has been Successfully bridged with ivory vigorously stirred solution, resulting in a colloidal suswhich also is itself replaced in time with living bone. pension f th organic lt d b t in d i a The present invention Provides stronger and more mixed solvent system which is comprised of acetone ily formed implants or prostheses which have bone red di h l lf xide placement characteristics im ar to ivory. Using the foregoing colloidal suspension as the elecin general, the Present invention Provides a method trolyte and an electrolytic apparatus comprising a of electrochemically depositing bone Particles and Pyrex glass reaction kettle with cover and two metal r i binder onto the external surface of a bone proselectrodes 2 X l X 0.02 inches, a coating is obtained on thesis to form a coating which stimulates bone attachth di l t d h a lt i li d t th ment. The organic binder is preferably O t e p ly mi metal electrodes. In a preferred embodiment process, acid family Such as Dupont y which n 300 ml of solution is used and the anode-to-cathode Cured Provides a Poiyimide of high thermal -h separation is maintained at 1 inch. The potential apand is inert to attack from most chemicals. plied between the electrodes is derived from a variable Accordingly, it is an object of the present invention voltage d w r supply and coatings of various thickt provide a method of enhancing bone growth on prosness and hardness are obtained and tested for mechanitheses by binding bone particles to a prosthesis. cal, physical and thermal properties,

Another object Of this invention s to Provide a Tests conducted on the coatings obtained according method of blending bone particles and a binder to proto h foregoing procedure h h f ll i h mote the formation of a coating of controlled thickness i l, ph ical and thermal properti of elect odeposon a prosthesis. ited Pyre-M.L. Pyre-M.L. is a 16.5% by weight solution A further object of this invention is to provide an imf an ti l lli i id i N h l 2 proved method of depositing bone and a plastic matelid lv t,

TABLE I Typical Value Property at 25C Test Method Folding endurance* Ultimate elongation Impact test Abrasion resistance Adhesion & flexibility Thermal aging Tensile strength* Coefficient of friction* 30,000 cycles ASTM D-882-64T 80 in-lb (direct Falling Ball and reverse) impact 400g Hoffman scratch test No cracking or loss of adhesion (1/16 Conical mandrel in. bend) Expected life l0.()00 AlEE Method 57 hr at 250C 24,000 psi ASTM D-882 0.42 ASTM D1505 Test evaluated on stripped film. Test evaluated on substrate (Cu and Al).

The effect of applied voltage on bone/Pyre-M.L. colloidal dispersions is shown in the following table. The test specimen consisted of 5 grams of bone contained in 50 ml Pyre-M.L., 10 ml triethylamine, 200 ml dimethylsulfoxide and 1,000 ml acetone. The coatings were cured to 300C in an oven for one hour.

TABL E II Applied Deposition Coating Voltage Time Thickness (volts) (secs) Anode mils Adhesion 50 60 steel -0. 5 good 5 O 60 steel 1 good 5 O 60 Cr 1 good l 60 Al -2 good 100 60 Cu -2 good The effect of electrodeposition time on various coating thickness of bone/Pyre-M.L. is indicated in the folcoating, the bone level appearing to be arbitrarily lim- I ited, to substantially Adhesion is excellent for coatings of 2 mils but deteriorates rapidly as coatingthicknesses of 10 mils are approached.

Other suitable aromatic polyamic acid polymers ca be represented by the recurring unit:

lowing table. The colloidal suspension contained 10 H O O grams of bone contained in 50 ml Pyre-M.L., 10 ml triethylamine, 200 ml dimethylsulfoxide and 1,000 ml ac- C OH etone. The coatings were cured to 300C in an oven for one hour.

TABLE III R .0 Applied Deposition Coating Voltage Time Thickness I (volts) (secs) Anode mils Adhesion HO-|(|I l--' 100 60 steel -l good I I I v 100 100 steel -2 good o O H 100 120 steel 5 good n 100 300 steel 10 very poor v in which n is at least 15.

Table IV below shows the results of applying various Suitable solvents for the polyamic acids are dimethyl voltages to varying weights of bone over varying depoacetamide, dimethyl formamide, N-methyl-Z sition times. In these tests, an organic matrix composipyrrolidone and dimethylsulfoxide. Preferred nontion of 50 ml Pyre-M.L., 10 ml triethylamine, 200 ml solvents, in addition to acetone, for the polyamic acid dimethylsulfoxide and 1,000 ml acetone was used and include methyl isobutyl ketone, methyl ethyl ketone, the coatings were cured at 300C in an oven for one methyl 'n-propyl ketone, diethyl ketone, mesityl oxide h V and cyclohexanone. Suitable bases, for salt-solution,

TABLE IV Approximate Weight of Applied Deposition Coating Bone Voltage Time Thickness I g V secs Anode mils Adhesion v 5 30 60 steel I I 0.5 good i 5 60 steel l good 5 50 60 Cr 1 good 5 100 60 Al 2 good 5 100 60 Cu 2 poor 10 50 120 steel 2 good 10 I00 l20 steel 5 poor 10 100 300 steel 10 very poor 25 50 30 steel 1 poor 25 100 60 steel 4 very poor 25 100 120 steel 6 very poor 25 100 300 steel 10 very poor Four different bone concentrations were investiinclude triethylamine, trimethylamine, N,N-dimethylgated. Under the influence of the electric field, bone benzylamine, N-ethylpiperidine, pyridine and 1- particles were transported within the organic matrix to' methylimidazole. the anode and deposited at this electrode. Concentra- The present invention thus teaches a process by tions of lower weights of bone produced cathode coatwhich bone and organic matrix may be simultaneously h1g5 which have good adhesion to the 511211111655 Steel adhered by electro-chemical deposition onto orthopesubstrate. When the concentration is increased twofold di i l ts, In the electro-deposition process, both 01' more, thicker coatings are obtained in all but one inbone particles and organic matrix are formed on the orstance but these coatings have P r 0 very P adhethopedic implant. The organic matrix, which is evenly sion properties. dispersed within the bone particles, is believed to pro- The best coatings for adhesion and thickness are mote healing at least partly because of the spacing of achieved utilizing a solution comprised of an organic the bone particles which makes them accessible to atmatrix of 50 ml Pyre-M.L., l0 t'riethylamine, 200 ml dimethylsulfoxide and 1,000 ml acetone. It appears that the mobility of Pyre-M.L., under the influence of the electric field, far exceeds that of the bone particles.

tachment of living bone within the matrix. In the preferred embodiment, electrodeposition of finely divided bone particles from polyamic acid dispersions onto metal substrates provides a basis for the preparation of prostheses for both joint and/or socket replacement, bone bridge, etc. These prostheses enhance bone repair rates by providing a coating to which living bone may adhere and which ultimately is completely replaced by living bone.

The electrodeposition process provides several advantages in the forming of superior prosthetic devices, one being a controlled thickness of electrodeposition and another being a uniform coverage of irregularly shaped substrates. The controlled thickness feature reduces the finishing required to produce a frictionless freely movable joint. A further advantage is obtained through the dissolution of the metallic electrode during electrodeposition.

The process of the invention is also rapid in relation to normal body processes or other forms of bone repair such as pins, clamps, etc. The process also is exceedingly economical since all of the compounds used therein are readily available and no complex equipment is required.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings.

What is claimed is:

1. A method of forming a prosthesis for bone repair or replacement comprising:

electrodepositing finely divided powdered bone particles from colloidal suspensions of said bone particles in a solution comprising acetone, dimethylsulfoxide, an organic amine and a polyamic acid onto a metallic substrate in the form of said prosthesis.

2. The method of claim 1 wherein the polyamic acid is taken from a group of aromatic polyamic acid polymers having the recurring unit:

in which n is at least 15.

3. The method of claim 2 wherein the polyamic acid is a 16.5% by Weight solution of an aromatic polymellitamic acid in N-methyl-2pyrrolidone solvent.

4. The method of claim 3 wherein said amine is taken from the group including triethylamine, trimethylamine, N,N-dimethylbenzylamine, N-ethylpiperidine, pyridine and l-methylimidazole.

5. The method of claim 4 wherein said solution is characterized by the presence of an organic salt of free carboxyl groups,

said solution heated to substantially 40C and maintained at said temperature for substantially minutes prior to initiating said electrodeposition.

6. A method of producing in orthopedic implant for enhancing bone repair rates in bone bridge and other bone operations comprising:

dispensing ground bone particles in a solution containing a polyamic acid and an organic salt in a solvent taken from a group including dimethyl acetamide, dimethyl formamide, N-methyl-Z- pyrrolidone and dimethylsulfoxide, and a nonsolvent taken from the group including methyl isobutyl ketone, methyl ethyl ketone, methyl n-propyl ketone, diethyl ketone, mesityl oxide, cyclohexanone and acetone so as to obtain a colloidal suspension of an organic salt and bone.

7. The method of claim 6 wherein said solvent is dimethylsulfoxide, said non-solvent is acetone and said solution is heated to substantially 40C and maintained at said temperature for substantially 15 minutes before initiating said electrodeposition.

8. The method of claim 7 wherein said implant is the anodic electrode of an electrolytic deposition system wherein a dc voltage of from 50 to volts is applied across the electrode thereof 9. The method of claim 8 wherein said organic salt is taken from the group triethylamine, trimethylamine, N,N-dimethylbenzylamine, N-ethylpiperidine, pyridine and l-methylimidazole.

10. A method of forming a prosthesis for bone repair or replacement comprising:

electrodepositing finely divided powdered bone particles from a colloidal suspension of said bone particles in an inert plastic binder onto a metallic substrate in the form of said prosthesis.

11. The method of claim 10 wherein the inert plastic binder is an organic matrix formed by a polyamic acid dissolved in a solvent:

an amine added to the solution to produce the organic salt of a free carboxyl group; and

said solution and said bone particles stirred into a non-solvent electrolyte so as to form a colloidal suspension of said organic salt and said bone particles in said solvent and non-solvent.

12. The method of claim 11 wherein said solution is heated to substantially 40C and maintained at said temperature for substantially 15 minutes prior to initiating said electrodeposition.

13. The method of claim 12 wherein said substrate is the anodic electrode of an electrolytic deposition system in which a dc voltage of from 50 to 100 volts is applied across the electrodes thereof.

14. The method of claim 13 wherein the polyamic acid is taken from a group of aromatic polyamic acid polymers having the recurring unit:

in which n is at least 15;

16. The method of claim 15 wherein the solvent is dimethylsulfoxide.

17. The method of claim 16 wherein the non-solvent is acetone.

18. The method of claim 17 wherein the amine is lmethylimidazole.

19; The method of claim 17 wherein the amine is triethylamine.

20. The method of claim 19 wherein the portions of the components are 5 grams bone, 50 ml polyamic acid, 10 ml triethylamine, 200 ml dimethylsulfoxide 

1. A METHOD OF FORMING A PROSTHESIS FOR BONE REPAIR OR REPLACEMENT COMPRISING: ELECTRODEPOSITING FINELY DIVIDED POWDERED BONE PARTICLES FROM COLLOIDAL SUSPENSIONS OF SAID BONE PARTICLES IN A SOLUTION COMPRISING ACETONE, DIMETHYLSUFLOXIDE, AN ORGANIC AMINE AND A POLYAMIC ACID ONTO A METALLIC SUBSTRATE IN THE FORM OF SAID PROSTHESIS.
 2. The method of claim 1 wherein the polyamic acid is taken from a group of aromatic polyamic acid polymers having the recurring unit:
 3. The method of claim 2 wherein the polyamic acid is a 16.5% by weight solution of an aromatic polymellitamic acid in N-methyl-2-pyrrolidone solvent.
 4. The method of claim 3 wherein said amine is taken from the group including triethylamine, trimethylamine, N,N-dimethylbenzylamine, N-ethylpiperidine, pyridine and 1-methylimidazole.
 5. The method of claim 4 wherein said solution is characterized by the presence of an organic salt of free carboxyl groups, said solution heated to substantially 40*C and maintained at said temperature for substantially 15 minutes prior to initiating said electrodeposition.
 6. A method of producing in orthopedic implant for enhancing bone repair rates in bone bridge and other bone operations comprising: dispensing ground bone particles in a solution containing a polyamic acid and an organic salt in a solvent taken from a group including dimethyl acetamide, dimethyl formamide, N-methyl-2-pyrrolidone and dimethylsulfoxide, and a non-solvent taken from the group including methyl isobutyl ketone, methyl ethyl ketone, methyl n-propyl ketone, diethyl ketone, mesityl oxide, cyclohexanone and acetone so as to obtain a colloidal suspension of an organic salt and bone.
 7. The method of claim 6 wherein said solvent is dimethylsulfoxide, said non-solvent is acetone and said solution is heated to substantially 40*C and maintained at said temperature for substantially 15 minutes before initiating said electrodeposition.
 8. The method of claim 7 wherein said implant is the anodic electrode of an electrolytic deposition system wherein a dc voltage of from 50 to 100 volts is applied across the electrode thereof.
 9. The method of claim 8 wherein said organic salt is taken from the group triethylamine, trimethylamine, N,N-dimethylbenzylamine, N-ethylpiperidine, pyridine and 1-methylimidazole.
 10. A method of forming a prosthesis for bone repair or replacement comprising: electrodepositing finely divided powdered bone particles from a colloidal suspension of said bone particles in an inert plastic binder onto a metallic substrate in the form of said prosthesis.
 11. The method of claim 10 wherein the inert plastic binder is an organic matrix formed by a polyamic acid dissolved in a solvent: an amIne added to the solution to produce the organic salt of a free carboxyl group; and said solution and said bone particles stirred into a non-solvent electrolyte so as to form a colloidal suspension of said organic salt and said bone particles in said solvent and non-solvent.
 12. The method of claim 11 wherein said solution is heated to substantially 40*C and maintained at said temperature for substantially 15 minutes prior to initiating said electrodeposition.
 13. The method of claim 12 wherein said substrate is the anodic electrode of an electrolytic deposition system in which a dc voltage of from 50 to 100 volts is applied across the electrodes thereof.
 14. The method of claim 13 wherein the polyamic acid is taken from a group of aromatic polyamic acid polymers having the recurring unit:
 15. The method of claim 14 wherein the polyamic acid is a 16.5% by weight solution of an aromatic polymellitamic acid in N-methyl-2-pyrrolidone solvent.
 16. The method of claim 15 wherein the solvent is dimethylsulfoxide.
 17. The method of claim 16 wherein the non-solvent is acetone.
 18. The method of claim 17 wherein the amine is 1-methylimidazole.
 19. The method of claim 17 wherein the amine is triethylamine.
 20. The method of claim 19 wherein the portions of the components are 5 grams bone, 50 ml polyamic acid, 10 ml triethylamine, 200 ml dimethylsulfoxide and 1,000 ml acetone. 